1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, and in particular to a highly sensitive, high-performance electrophotographic photoreceptor having a photoconductive layer that contains organic photoconductive materials.
2. Discussion of the Background
Conventionally, inorganic photoconductive materials, such as selenium, cadmium sulfide, and zinc oxide, have been widely used for photosensitive layers of electrophotographic photoreceptors. These known materials, however, have the following disadvantages: selenium and cadmium sulfite need to be disposed of as toxicants, selenium becomes crystalline upon heating, and thus has a poor heat resistance, cadmium sulfide and zinc oxide have poor moisture resistance, and zinc oxide has an extremely low resistance to repeated printing operations. Thus, considerable efforts have been put into development of novel photoreceptors. In recent years, extensive studies have been conducted on the use of organic photoconductive materials for photosensitive layers of electrophotographic photoreceptors, and some of such materials have been put in practical use. Compared to known photoconductive inorganic materials, organic photoconductive materials are advantageously light-weight, innocuous or non-poisonous to environments, form films easily, and facilitate the manufacture of photoreceptors. In addition, the use of an organic photoconductive material makes it possible to produce a transparent photoreceptor, depending upon the type of the material.
Recently, so-called function-separation-type photoreceptors, in which different types of compounds are respectively used to perform the separate functions of charge carrier generation and charge carrier transportation, have been developed, and photoreceptors of this type using an organic material(s) have been used. For charge carrier transport material a high molecular weight polymeric photoconductive compound, such as polyvinyl carbazole, is used in some applications, and a low molecular weight photoconductive compound that is dispersed or dissolved in a binder polymer is used in other applications.
In particular, the use of such a low-molecular weight organic photoconductive compound makes it easy to provide a photoreceptor having excellent mechanical characteristics, since a polymer having high film-formability, flexibility, and adhesive property, may be selected as a binder, as disclosed in, for example, unexamined Japanese Patent Publication (Kokai) No. 63-269160, and examined Japanese Patent Publications No. 3-39306 and No. 4-53308. However, it has been difficult to find a compound that is suitable for producing a photoreceptor having a sufficiently high sensitivity.
U.S. Pat. No. 5,338,633 discloses an electrophotographic photoreceptor comprising a photoconductive layer containing the following compound: ##STR2## In the compound, --O--X--O-- is bonded to two phenyl groups at positions para to nitrogen atoms bonded to the phenyl groups. In contrast, the compound of formula (I) of the present invention has a --O--Y--O-- group bonded to two phenyl groups at positions meta to nitrogen atoms bonded to the phenyl groups.
JP-A-5-210251 discloses an electrophotographic photoreceptor comprising a photosensitive layer containing a compound of the following formula: ##STR3## where Ar.sub.1, Ar.sub.2, Ar.sub.3, Ar.sub.4, Ar.sub.5 and Ar.sub.6 each represent an aryl, biphenyl or heterocyclic group that can be substituted or unsubstituted, and R represents an alkylene group, a aralkylene group, and alkelene group or a heterocyclic group. In the above formula, --O--R--O-- can be bonded to the adjacent Ar.sub.3 and Ar.sub.4 at any position relative to the respective nitrogen atoms. However, the specific compounds disclosed in JP-A-5-210251 have --O--R--O-- bonded to adjacent Ar.sub.3 and Ar.sub.4 only at positions para to the respective bonded nitrogen atoms.
There is a need for a photoconductive compound that is suitable for producing a high sensitivity electrophotographic photoreceptor.